Several coupling devices for tractors are known. A compilation of such, utilized or just suggested is given in the Swedish Patent Application SE- 8104211-1, published as laid open publication No. 434 000 on 1984 Jul. 2nd. In this publication coupling devices of all conceivable types are described, also of the art mentioned introductorily. There is also a list of the demands for such coupling devices. Among those demands may be mentioned:
possibility to couple the tools quickly and easily, PA1 possibility to adjust the coupling easily and simply.
Among the described couplings some are very complicated and expensive, and furthermore they do not meet said two demands.